The production of semiconductor wafers, substrates and photomask plates used in the manufacture of semiconductor wafers, has typically utilized processing equipment in which various types of processing fluids are used to treat the wafers. One example of a semiconductor processor is a centrifugal rinser-dryer used to rinse acids, caustics, etchants and other processing fluids from wafers, photomask plates, and similar flat media.
The rinser-dryers are also used to dry the rinsed units using a flow of heated gas, such as nitrogen, which is passed through the processing chamber after rinsing with the desired fluid. The wafers are spun during processing to provide more even distribution of the processing fluids across the wafer surfaces, and to assist in removal of rinsing liquids in preparation for drying.
Other types of semiconductor processors include acid, solvent, and caustic treatment machines which spray or otherwise apply acids, solvents and caustics to the wafers or other flat media. Stripping processors are used to remove photoresist from the wafers. Other specific processing of semiconductors may require other types of chemicals. Many of these processes are performed in centrifugal processing machines to provide for even distribution of fluids over the wafer and to aid in removal of liquids.
A primary problem in the production of semiconductors is particle contamination. Contaminant particles can affect the photographic processes used to transfer the chip layouts onto the wafers being processed into chips. Contaminants on the photomasks can cause deterioration of the image being transferred onto the wafer. The direct processing of the wafers themselves is even more susceptible to contamination because of the numerous processing steps involved and the risk at each stage that contaminating particles can become adhered to the surface of the wafer. Particle contamination causes a large number of the chips in a wafer to be defective. Thus it is very important to reduce contamination to increase yields.
With the high resolution now made possible through newer semiconductor processing techniques, the effects of contaminants have become even more significant and problematic than in the past. Previously, contaminant particles smaller than 1 micron did not result in defects due to minimum feature sizes of 2 microns or more. However, now the feature size used in high density chip designs is substantially less, e.g., 0.18 micron. Even higher density chips with even smaller feature sizes are expected in the future. The move toward smaller feature size is compounding the contamination problem because of the greater difficulty in controlling smaller particles in the environment. If contaminants are present then substantial numbers of the resulting chips can be rendered defective and unusable, at substantial costs to the manufacturer.
The causes of contaminating particles on wafer surfaces occurs from numerous sources. Each of the processing fluids used is necessarily impure to some small degree. The water used in processing is deionized to remove metallic ions and other impurities, but such supplies also contain some impurities. Centrifugal processing is advantageous because spinning the wafers or other flat media flings off fluid droplets. This helps to prevent contamination by "spotting" which occurs if fluid droplets on the wafer evaporate. It is also advantageous to have the used rinse water or fluids removed from the processing chamber as quickly as possible, to prevent recontamination.
Centrifugal processors, such as spray solvent and spray acid processors, and spin rinser dryers, typically have a rotor which spins inside of a cylindrical processing chamber or bowl. The cylindrical rotor holds a removable cassette or non-removable combs which carry the wafers. As shown in FIG. 2, and as described in U.S. Pat. No. 5,022,419, incorporated herein by reference, the bowl typically has a drainage ditch or channel running from the front to the rear, near the bottom of the bowl, to drain fluids out of the bowl. These types of centrifugal processors have been used very successfully in semiconductor manufacturing.
However, in these types of centrifugal processors, the spinning rotor, which is centered in the bowl, generates rapid counter-clockwise air movement within the bowl. This air movement hinders the clean drying or other processing operation of the centrifugal processor, as it tends to draw spent fluid droplets of e.g., water, solvent, or acid, up and around in the bowl, allowing droplets to be re-deposited on the wafers or other flat media. The air movement also tends to draw droplets away from the drainage channel, allowing them to be disadvantageously recycled back up and around the bowl.
Accordingly, there remains a need in semiconductor manufacturing for improved centrifugal processing machines.